Air-steam and oxy-steam gasification of hydrolytic residues from biorefinery

This paper reports the use of lignin-rich solid, derived from enzymatic hydrolysis of lignocellulosic biomass, to produce syngas and pyrolysis oil. The tested process was an updraft gasification carried out at pilot scale of about 20 kg/h as solid feed. The reactivity of two residues, one from straw and one from cane, was investigated by TGA in air, oxygen, nitrogen, using a heating program simulating the thermal gradient in the gasifiers. Below 400 degrees C the residues completely burned in air or oxygen with an apparent reaction order of 0.1-0.2. The 75%-80% of the organic mass was pyrolysed at 700 degrees C, when the gasification with H2O and CO2 started. In the plant tests, the residue was completely converted in gaseous and liquid energy carriers with an overall energy efficiency of up to 87%. Ten conditions were examined with different air flow (19.0, 25.5, 26.5 kg/h), 02 (4.0, 4.5, 5.5 kg/h) or H2O (as steam at 160 degrees C: 1, 2.5, 4.0, 4.5, 5.5, 8.5 kg/h). The experimental data were analyzed using the Response Surface Analysis (RSA) in order to highlight the dependence on the Equivalence Ratios of oxidation. The molar ratio H-2/CO in the syngas increased by using steam as co-gasification agent, and reached the value of 2.08 in oxy-steam gasification. Steam was necessary to stabilize the process when rising oxygen as it was effective in lowering the average temperature in the gasifier. Another positive effect of using steam was the shift of the temperature maximum far from the grate where ash melting could occur. Oxy-steam gasification provided the best results in terms of syngas heating value (LHV 10.9 MJ/m(3)) and highest thermal power output of the plant (67 kW(th)). The tar yield was inversely correlated with the residence time of the gas in the bed, in according with a zero order reaction for tar cracking into incondensable hydrocarbons and hydrogen.